Abstract: This work in philosophical theology argues that the concept of panentheism (literally, “all [is] in God”) is crucial for understanding Tillich’s doctrine of God, as it painstakingly explicates relevant Tillichian expressions, including his famous claim that “God is not a being.” Distinguishing between an active and passive aspect of God in panentheism, it further argues that self-avowed panentheist Hartshorne, by adopting Whitehead’s notion of causality, is not panentheistic with respect to the active aspect of divine power. Avoiding pitfalls of Hartshorne regarding the active aspect and Tillich regarding the passive aspect, it offers a creative synthesis, a full-fledged panentheism that attempts to do justice to divine receptivity, suffering and temporality as well as to divine sovereignty, majesty, and ultimacy.